This invention is concerned with a method for production of maltose and a limit dextrin, whereby raw starch is treated with an amylase, whereafter the maltose and the limit dextrin are recovered, the limit dextrin, and a use of the limit dextrin.
Maltose is a disaccharide, which is used in huge amounts in the candy industry. Maltose does not crystallize easily, in contradistinction to e.g. glucose, which is able to crystallize even in the presence of impurities in high concentrations. Maltose is not able to crystallize and thus to be purified further, unless the maltose used as a starting material exhibits a purity above 90%. Also, the fact that maltose does not crystallize easily is one of the reasons why maltose is a valuable raw material in the candy industry.
Maltose has also other applications, e.g. as the active component of intravenous injection liquids intended for provision of sugar for the patient and as a component in frozen deserts (due to the fact that the crystallization ability of maltose is very little), in the baking and brewing industry, and for production of maltitol, which can be used as a sweetening agent, like sorbitol, vide Glycose Sirups, Science and Technology, Elsevier Applied Science Publishers 1984, pages 117-135.
The prior art methods for production of maltose suffer from the disadvantage that they are rather cumbersome, especially if the maltose has to be prepared in a purity above 90%.
Thus, reference can be made to 44. Stxc3xa4rke-Tagung 21-23 April 1993 (reprint from BioTimes No. 4/93, edited by Novo Nordisk), and Die Stxc3xa4rke, 36 (1984), 405-411, Helle Outtrup and Barrie E. Norman. From the first of these two publications it appears that the maximum obtainable purity of maltose (when a mixture of three enzymes is used) is 80%, and from the second of these two publications it appears (page 10) that the maximum obtainable purity (at the highest enzyme dosage) is about 70%.
Thus, the purpose of the invention is the provision of a method for production of maltose, of the above indicated kind, which is simpler and cheaper in comparison to the prior art methods for production of maltose and in relation to which maltose can be obtained in a purity well above the purity obtainable according to prior art methods, i.e. a purity above 90%, and, as a spin-off effect, the provision of a new limit dextrin, and a use thereof.
The method according to the invention for production of maltose and a limit dextrin, whereby raw starch is treated with an amylase, whereafter the maltose and the limit dextrin are recovered, is characterized by the fact that the amylase is a hydrolase with the enzyme classification EC 3.2.1.133, that the temperature is lower than the lowest temperature at which the raw starch is gelatinized, and that the recovery of the maltose and the limit dextrin is performed as an ultrafiltration, whereby the maltose is in the permeate, and the limit dextrin is produced as the solid phase by liquid-solid separation of the retentate.
As indicated, the recovery of maltose is carried out as follows. After treatment of the raw starch the solid phase and the supernatant therefrom comprising mainly oligosaccharides and maltose is subjected to an ultrafiltration, which yields a permeate, the dry matter of which contains more than 90% of maltose. Centrifugation or filtration of the unreacted raw starch can be carried out in a step before the ultrafiltration step, if wanted.
The gist of the invention, thus, is the recognition that a category of amylases exists, which is able to give rise to a degradation product of raw starch, which consists of a mixture of maltose and high molecular oligosaccharides, which mixture by simple ultrafiltration gives rise to a permeate with a dry matter consisting of more then 90% maltose. This is surprising because the prior art degradation products of raw starch, formed by means of amylases, comprises relatively large amounts of low molecular sugars, such as glucose and maltotriose, which would lower the purity of the maltose in the permeate far below 90%.
It goes without saying that the pH during the method should be at or in the vicinity of the pH optimum of the amylase used for the production of maltose.
EP 350737 describes a process for production of maltooligosaccharides comprising mainly maltose and maltotriose by use of raw starch as a starting material and with a specific Bacillus stearothermophilus amylase as the starch degrading enzyme. However, the classification of this Bacillus stearothermophilus amylase is not EC 3.2.1.133, and it clearly appears from the specification of EP 350737 that it is not possible to produce the maltose in a purity above 90%.
Also, according to the invention it has been found that the limit dextrin, which prima facie would be considered a waste product has applicability as a fat replacer in foods.
A preferred embodiment of the method according to the invention is characterized by the fact that the raw starch is waxy maize starch. With waxy maize starch a high yield is obtained, and also, the reaction proceeds smoothly, due to the fact that the viscosity of the reaction mixture is low.
A preferred embodiment of the method according to the invention is characterized by the fact that the hydrolase with the enzyme classification EC 3.2.1.133 is a B. stearothermophilus amylase with a molecular weight of 70,000xc2x15,000. Reference is made to the paper xe2x80x9cProperties and application of a thermostable, maltogenic amylase, produced by a strain of Bacillus modified by recombinant-DNA techniquesxe2x80x9d by Helle Outtrup and Barrie E. Norman of Novo Nordisk A/S, Die Stxc3xa4rke, 36 (1984), 405-411, in which this amylase is described. In this paper the prior art amylase is used exclusively in connection with liquefied starch as a starting material, and it has not been possible to prepare a final product with a purity above 90% by means of this prior art method.
A preferred embodiment of the method according to the invention is characterized by the fact that the ultrafiltration is carried out simultaneously with the treatment of the raw starch with the amylase, and that the temperature is above 40xc2x0 C. In this manner the process time can be reduced, and also, the yield of the maltose in the permeate is improved.
Also, the invention comprises the limit dextrin, prepared as in the method according to the invention. If for some reason, the limit dextrin in a specific context is the important product, and the maltose is of no significance, the ultrafiltration is unnecessary, as the limit dextrin can be produced directly after the amylolytic degradation by solid-liquid separation of the amylolytic degradation mixture and by washing of the solid phase. Besides being characterized by the fact that it is produced by means of the method according to the invention the limit dextrin according to the invention is characterized by the fact that the ratio xcex1-1,4 bonds/xcex1-1,6 bond s is smaller than for the raw starch (which is consistent with the assumption that the special amylase only cleaves the xcex1-1,4 bonds of the starch), that the DE is 6.3 for waxy maize starch and 7.9 for common corn starch, and that the molecular weight distribution is similar to the molecular weight distribution of the native, raw starch, but with a somewhat lower average value. The above indicated characterization by means of the ratio xcex1-1,4 bonds/xcex1-1,6 bonds can be quantified as follows: this ratio is 9 for the limit dextrin derived from the waxy maize starch and 20 for the genuine waxy maize starch, and it is 13 for the limit dextrin derived from the common corn starch and 50 for the genuine common corn starch. Due to the fact that the limit dextrin according to the invention prima facie would be considered a waste product, it is very cheap.
Finally, the invention comprises the use of the limit dextrin according to the invention as a fat replacer in foods. Surprisingly it has been found that this very cheap limit dextrin can be used as a fat replacer, which exhibits the same good organoleptic properties as traditional fat replacers. Also, the limit dextrin according to the invention can be used in confections with a gum structure, in soft drinks, in viscous dairy products, and as a carrier for dried liquids.
The invention will be illustrated in the following examples. In the examples the content of dry substance (DS) in the starch slurry is 25% (Example 1) and 20% (Example 2). The DS content in relation to this invention advantageously can have a value between 10% and 50%, preferably between 20% and 40%.